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Temperate Rain Forests of the Pacific Northwest

Assessing Vulnerability and Adaptation Measures

By Amber Dindorf

A Unique and Threatened Ecosystem

The temperate rainforests of the Pacific Northwest exist to the west of the Cascade Mountains and span 4000 kilometers from northern California to Alaska (O'neel et al., 2015). These forests west of the cascades are characterized by populations of evergreen trees like douglas fir, western hemlock, and pacific silver pine, sitka spruce, and coniferous trees such as maples, alders, and cottonwoods that receive consistent rainfall averaging from 200 to 700 centimeters in the rainforest areas of the coast (Temperate Rainforests 2018). These coastal rainforests are located in a small band that is bound by the Cascade Mountains and the Pacific Ocean that ranges from sea level to below the treeline about 1500 to 1700 meters above sea level (Mote P.W. et al., 2003). These forests are home to some large amounts of old growth which are very important for carbon sequestration.

https://www.youtube.com/watch?v=I63NLF2lDCw

Mossy Tree Trunk

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Old growth forests in the Pacific Northwest are praised for their massive trees that are hundreds and in some cases over 1000 years old (Temperate Rainforests, 2018). Some of these forests have turnover rates ranging from 350 to 950 years allowing trees to create biodiversity hotspots and more biomass (Lertzman et al., 1996). This is significant because these forests become important habitats to many species and forests with larger biomass are considered to be larger carbon sinks, meaning they play an important role in mitigating the impacts of climate change (Luyssaert et al., 2008). In addition to important ecological services there are also many people who rely on these forests for recreation and resources. Indigenous communities of this area including the Umatilla and the Quinault have had a long standing relationship with the forests and they have relied on the uses of 300 different species for food and medicinal purposes (Charnley et al., 2007). In addition to this, there is also a sacred appreciation of coastal rainforests in this area.

Threats Posed by Climate Change

Increased Precipitation and Temperature

Factors such as atmospheric circulation from the arctic, decreases in westerly winds, ocean absorption of excess heat, and the introduction of greenhouse gases into the atmosphere are impacting the climate in the Pacific Northwest (USGCRP, 2017). Average warming for this area was 1.3 degrees fahrenheit from 1895 to 2011 and it is projected that there will be an increase in the average annual temperature from 3.3 to 9.7 degrees fahrenheit by 2070 to 2099 (National Climate Assessment, 2014). Precipitation is projected to change from a decrease of 11% to an increase of 12% from 2030 to 2059 and decrease by 10% to an increase of 18% for 2017 to 2099 (National Climate Assessment, 2014).

Trees of the rainforests are often dripping with moss

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Decreasing Snowpack in the Cascades

The Cascade Mountains

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Warmer temperatures and seasonal temperature changes will likely result in shifting in elevation, earlier melting and overall decline of the alpine snowpack in the Cascade mountains (Mote P.W. et al., 2003). This has already started to happen and as a result there have been significant impacts to the hydrological systems of the Pacific Northwest such as streamflow decline and increased rates of drought (USGCRP, 2017). Temperate rainforests often receive 870 cubic kilometers of freshwater flow from the mountains and it is predicted that this average will greatly decline by the end of the century (O'neel et al., 2001).

Forest Fire

Forest Fire in the Rainforests of the Pacific Northwest

nps.gov

Though it may seem unlikely that a rainforest ecosystem is susceptible to the forest fires that have been raging to the south, there are several climate variations that could increase exposure to forest fires. Forest fires are correlated to the melting of the nearby snowpacks in the west and with reduced snow melt, the soils in the areas west of the Cascade Mountains have become dry and this trend is likely to continue (Westerling et al., 2006). One predicted result of increased warming in the temperate rainforests is an increased growing season, but this coupled with periods of drought can create more fuel and increase risk for forest fires (Dale V.H. et al., 2001). In 2015 there was a forest fire in Olympic National Park, one of the wettest places in the United States due to decreased snow melt and drought conditions (Banerjee, 2015).

Increase in Invasive Species

New climate patterns of warmth will have an impact on species distribution and the presence of insects and diseases for coastal temperate rainforests in the Pacific Northwest. Warmer climates, like those predicted for the coastal forests of the northwest create an increase in insect populations and diseases that can be harmful to trees (USGCRP, 2017). Increases in spruce budworm populations that impact the western hemlocks and sitka spruce trees in the rainforests as well as other defoliator insects and pathogens that can damage mycorrhizal fungi which creates a sharing network between trees are likely to continue (Dale V.H. et al., 2001).

Spruce Budworms threaten many Tree Species

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Assessing Vulnerability and Adaptation

This area is vulnerable to the threats described above. Old growth forests are fairly resilient ecosystems due to their nutrient rich soil and diversity. This ecosystem is most susceptible to increased amounts of precipitation, increased rates of wildfire and insect infestation (National Climate Assessment, 2014). Coastal rainforests will continue to experience exposure to warmer temperatures, drought as a result of decreased snow melt, disease, changes in consistent precipitation, and in some cases forest fires (USGCRP, 2017). Although the exposure is not as severe as other regions to the south and east to the same factors, their limited resilience and the importance of these coastal temperate rainforest ecosystems cannot be ignored and therefore risk to these forests must be further evaluated with adaptation strategies.

Small insects like the spruce budworm can enter areas on firewood or other forest products. On the east coast of the United States there is a ban on importing firewood from outside states. Although these insects are already in the region increased monitoring can help forests at risk. Others propose landscape alteration that decreases migration of insects and disease (Spies et al., 2009).

Increased protection for forest ecosystems

Increased protection that is founded on traditional ecological knowledge will increase this ecosystems resilience. Forests management directed at plant establishment phases, increasing forest genetic diversity, and connectivity between forests will be the most effective (Millan et al., 2007).

Sources

Banerjee, S. (2015, July 31). The Wettest Rainforest in the United States Has Gone Up in Flames. Retrieved March 01, 2018, from https://www.thenation.com/article/the-wettest-rainforest-in-the-united-states-has-gone-up-in-flames/

My name is Amber and this website was created as a part of the 2018 Adapt Climate Change Course. I was a double major between Environmental Studies and Global Studies and I am particularly interested in forest ecology.